State Sen. Mike Gabbard switched political parties yesterday and became a Democrat, explaining that he believes he can be more effective to his constituents as part of the majority in the Senate.

"It took a lot of soul-searching," Gabbard, D-19th (Kapolei, Makakilo, Waikele), said at an afternoon news conference at Democratic Party of Hawai'i headquarters, where he was flanked by his wife, Carol, his family, and party, Senate and labor union leaders.

Gabbard's switch leaves four Republicans in the Senate compared to 21 Democrats.

Gabbard, who gained prominence as an opponent of same-sex marriage in the 1990s, described himself as a social conservative who disagrees with the party's platform in favor of civil unions and abortion rights. But the senator is with the party on labor and environmental issues and said he fits within its big-tent political philosophy.

"There are obviously some things we don't see eye to eye on," Gabbard acknowledged, adding that he would continue to be independent and not always follow the party line on votes.

Word of Gabbard's possible switch had caused an internal debate over what the party stands for and how much elected Democrats are expected to follow its platform. Many gay and progressive activists vividly remember Gabbard's often polarizing role in the campaign that led to a constitutional amendment against same-sex marriage in 1998.

Gabbard met privately with about 20 party activists on Saturday afternoon at party headquarters for what was described as a respectful but pointed discussion. According to several people who attended, Gabbard apologized if he had ever offended or caused pain to anyone by his comments in the heat of political battle.

Gabbard was questioned not only about same-sex marriage, according to participants, but of his past support for President Bush, his opposition to abortion rights, his thoughts on equal rights for women, and his religious affiliation.

Some activists were not satisfied. "Prejudice is not fit for any political party," said Doug Pyle, the co-chair of the party's legislation committee.

Mike McCartney, the party's chairman, said the reaction to Gabbard's switch within the party has been mixed. But the state senator was treated warmly yesterday by McCartney, U.S. Sen. Daniel Akaka, state Senate President Colleen Hanabusa, D-21st (Nanakuli, Makaha), and state Sen. Norman Sakamoto, D-15th (Waimalu, Airport, Salt Lake).

Gabbard's daughter, Tulsi Gabbard Tamayo, is a former Democratic state representative and a Washington, D.C., aide to Akaka. Akaka said the party accepted Gabbard with a "spirit of aloha."

"The Hawai'i Democratic Party has never turned people away," McCartney said. "It goes back to the plantation days. We're inclusive."

Gabbard served on the City Council and ran unsuccessfully as a Republican for U.S. Congress against Ed Case in 2004. He was elected to the Senate last year.

During his first session, Gabbard was more likely than other Republicans to vote with Democrats and went with the majority party on some key overrides of Gov. Linda Lingle's vetoes.

Lingle, according to a spokesman, believes Gabbard has done a disservice to the people who voted for him and supported him as a Republican by switching parties in the middle of his four-year term. The Republican governor also believes it is another example of the need for a strong two-party system so that Republicans do not think they have to become Democrats to get bills heard or to be effective.

State Senate Minority Leader Fred Hemmings, R-25th (Kailua, Waimanalo, Hawai'i Kai), said Gabbard had left to join a party Hemmings believes has not improved public education or diversified the economy despite being in power for a half-century.

"The political landscape is littered with those who thought they would become more politically effective by joining the Democratic Party," Hemmings said. "And what they've become effective at is maintaining a stranglehold on a political monopoly."

Hanabusa, who is trying to manage competing factions of Senate Democrats, described Gabbard as an asset as a Republican last session and said she was proud to welcome him to the party. She joked that she and Sakamoto were wondering when he would switch.